1. Field of the Invention
The present invention relates to a seal member adapted to be mounted between a cylinder head cover and an ignition plug tube.
2. Description of the Prior Art
Conventionally, a cylinder head of an engine is formed with an ignition plug tube insertion opening for insertion and mounting of an ignition plug tube. In the case where a cylinder head cover has a configuration that it lies over a substantially entire upper portion of a cylinder head, an ignition plug tube must be mounted inside the cylinder head cover and opened to the outside. With an engine of such type, a seal member is ordinarily mounted between the ignition plug tube and the cylinder head cover to seal blowby gas and scattered oil in the cylinder head cover from the outside.
FIG. 6 shows a conventional seal member 101 mounted between a cylinder head cover 102 and an ignition plug tube 108. The seal member 101 is formed of rubber, the elasticity of which presses a lip portion 106 against an underside of the cylinder head cover 102 to provide sealing between the cylinder head cover 102 and the ignition plug tube 108. In order to preserve the sealing performance, the seal member 101 must be preferably and closely contacted with the cylinder head cover 102 and the ignition plug tube 108.
However, when a distance L between an upper end of the ignition plug tube 108 and the surface of the cylinder head cover 102 contacting the seal member varies due to manufacturing reasons, and vibrations and thermal deformation of the cylinder head cover, closely contacted state between the lip portion 106 of the seal member 101 and the cylinder head cover 102 is degraded in quality, and hence the sealing performance becomes insufficient.
A seal construction for improving the sealing performance has therefore been developed, an example of which is disclosed in JP-A-62-195643.
In the disclosed seal construction, an annular stepped portion is provided around an ignition plug tube insertion opening of an cylinder head cover. The annular stepped portion has a peripheral surface, which extends in parallel with an outer peripheral surface of an upper end of the ignition plug tube at a location spaced from the outer peripheral surface. A seal member is mounted between the peripheral surface of the annular stepped portion and the outer peripheral surface of the ignition plug tube.
As shown in FIG. 7, the seal member 101 comprises a lip portion 116 extending annularly around the outer peripheral surface 108a of the ignition plug tube 108 to be pressed against the outer peripheral surface, an annular spring 110 provided on the lip portion 116 for pressing the same against the outer peripheral surface 108a of the ignition plug tube 108, a mount portion 117 mounted on the peripheral surface 104a of the annular stepped portion 104 of the cylinder head cover 102, and a bellows portion 118 connecting the mount portion 117 with the lip portion 116 and deformable so as to accommodate a change in spacing between the outer peripheral surface 108a of the ignition plug tube 108 and the peripheral surface 104a of the annular stepped portion 104.
In this seal construction, the seal member 101 is mounted on the peripheral surface 104a of the annular stepped portion 104 of the cylinder head cover 102, and the annular spring 110 presses the lip portion 116 against the outer peripheral surface 108a of the ignition plug tube over an entire periphery thereof. Accordingly, dispersion in distance between the cylinder head cover 102 and the ignition plug tube 108, as viewed in an axial direction of the ignition plug tube 108, does not affect the sealing performance therebetween. Further, even when the ignition plug tube 108 becomes somewhat eccentric relative to the peripheral surface 104a of the annular stepped portion 104, the sealing performance is not damaged since the bellows portion 118 deforms to accommodate the eccentricity.
However, since the conventional seal member shown in FIG. 7 comprises the bellows portion between the lip portion and the mount portion, the diametrical dimension is increased. Thus, there has been encountered a problem that the seal member and its surrounding structure are increased in size, and hence compact and lightweight device is unobtainable and freedom in design is impeded.
There has therefore been encountered a problem that, in the case where a cylinder head cover is formed of resin, there is a fear of the seal member falling off from the annular stepped portion due to thermal deformation of the cylinder head cover or the like.
It is an object of the invention to provide a seal member for solving the above-mentioned problems of the prior art.
To solve the above-mentioned problems, the invention provides a seal member adapted to be mounted between a cylinder head cover and an ignition plug tube, comprising a mount portion formed to be at least partially smaller in diameter than an inner diameter of a peripheral surface of an annular stepped portion formed around an opening of the cylinder head cover for insertion of the ignition plug tube, the mount portion being adapted to be interposed between an upper surface of the annular stepped portion and a baffle plate fused to an underside of the cylinder head cover to be radially movable, a first annular seal portion projecting radially outward from the mount portion to be brought into contact with the peripheral surface of the annular stepped portion, and a second annular seal portion projecting radially inward from the mount portion to be brought into contact with a peripheral surface of the ignition plug tube to be elastically deformable following relative radial movements between the mount portion and the ignition plug tube.
The seal member according to the invention having the above-described construction is interposed between the upper surface of the annular stepped portion of the cylinder head cover and the baffle plate to be surely mounted. Further, since the first seal portion and the second seal portion are brought into sealing contact with the peripheral surface of the annular stepped portion and the peripheral surface of the ignition plug tube over entire peripheries thereof, it is possible to provide a reliable sealing between the cylinder head cover and the ignition plug tube. For example, even when a position, in which the ignition plug tube is mounted, varies in an axial direction, the sealing performance is not damaged. When the ignition plug tube becomes eccentric relative to the peripheral surface of the annular stepped portion, the second seal portion is elastically deformed following such eccentricity and the mount portion moves radially. Accordingly, the change in a spacing between the ignition plug tube and the peripheral surface of the annular stepped portion, which is caused by the eccentricity, is accommodated and hence the sealing performance is maintained. The construction that the mount portion is thus radially movable brings about an advantage that the seal member can be made small in a diametrical dimension as compared with a conventional device provided with a bellows as shown in FIG. 7.
Preferably, the second seal portion is reinforced near an outer peripheral portion thereof with a reinforcement ring. With such structure, it is possible to prevent abnormal deformation of the seal member caused upon insertion of an ignition plug tube into a cylinder cover and at the time of an increase in inner pressure in the cylinder cover. It is also possible to restrict a direction, in which the seal member is deformed, when the ignition plug tube becomes eccentric. Further, since the portion to be deformed is divided into the portion of the second seal portion located on an inner periphery side with respect to the reinforcement ring and the mount portion located on an outer periphery side with respect to the reinforcement ring, it is possible to prevent occurrence of partially excessively deformed portions on the seal member.
Preferably, the first seal portion is formed to have a shape of a lip. By doing so, forces radially acting when the ignition plug tube becomes eccentric can be relaxed to facilitate radial movements of the mount portion, and there is no need of accurately prescribing dimensional tolerances of the annular stepped portion, which makes workability in assembly favorable. Also, a change in amount of sealing, caused by thermal deformation or the like, can be suitably accommodated.
A circumferentially continuous projection or circumferentially discrete projections may be formed on an end of the mount portion located on the side of the baffle plate to be brought into contact with the baffle plate. With such structure, a contact area between the mount portion and the baffle plate is reduced and hence a friction therebetween is reduced. It is therefore possible to facilitate radial movement of the mount portion while securely holding the mount portion between the upper surface of the annular stepped portion and the baffle plate. Further, since the holding force acting on the mount portion interposed therebetween is reduced, operation for fusing the baffle plate to the cylinder head cover is facilitated.
Such structure may be adopted that a circumferentially continuous annular projection or circumferentially discrete annular projections are formed on the cylinder head cover to extend from the upper surface of the annular stepped portion inwardly of the cylinder head cover, and an inner peripheral surface of the mount portion is fitted onto the annular projection or projections. With such structure, a state, in which the seal member is mounted, can be made stable.
Other objects, features and advantages of the invention will become apparent from the following description of embodiments of the invention made in conjunction with the accompanying drawings.